This invention relates to the fabrication of thin film oxides.
While oxide films can be grown using electron beam heating of the oxide source, the dissociation of the oxide results in a high background pressure of O.sub.2 in the chamber. Moreover, when an element is evaporated in an oxygen ambient, a very high O.sub.2 background pressure or very slow growth rate is necessary to form an oxide because of the short residence time of O.sub.2 on the growth surface.
Another approach to growth of an oxide (e.g., Al.sub.2 O.sub.3) employs a Molecular Beam Epitaxy (MBE) chamber to evaporate the metal (e.g., Al) in a background of about 10.sup.-5 Torr of O.sub.2. However, there are several difficulties associated with this approach. First, the high O.sub.2 background will oxidize the hot filaments of the effusion cells, ion gauges, etc. as well as the evaporation charges. Secondly, the O.sub.2 will react with the hot elements in the chamber to form high levels of CO and CO.sub.2, which could lead to undesirable carbon incorporation into the films. Finally, the kinetics of the reaction of Al with O.sub.2 are slow enough that the growth rate must be very slow or the O.sub.2 pressure very high so that the Al will fully oxidize. For example, R. W. Grant et al attempted to grow Al.sub.2 O.sub.3 in an ambient of 10.sup.-4 Torr of O.sub.2 by evaporating Al at a rate of 1 A/sec at a growth temperature of 25.degree. C. They reported in AFWAL-TR-80-1104, p. 25 (1980) that a metallic Al layer resulted with "no obvious difference from Al deposited under UHV conditions with no O.sub.2 ambient".